a. Field of the Invention
The present invention relates generally to orthotic devices for use in shoes, and, more particularly, to an orthotic insert in which there is a stationary heel post and a separate plate member which is pivotable thereon so as to provide a controlled range of motion for the foot.
b. Background Art
Orthotic devices have long been employed with considerable success to treat conditions or otherwise enhance the functions of the human foot, whether for ordinary walking or for various forms of specialized activities, such as skiing, skating, running and so on.
One form of such device has been a built-up structure in which there is a generally rigid, but still somewhat resiliently flexible plate, which usually extends from the heel of the foot to the metatarsal head area (i.e., the area beneath the metatarsal heads of the five phalanges), and a thick, vertical post which is fixedly mounted to the heel end of the plate. Typically, the orthotic plate is constructed of a thin, generally rigid material, such as fiberglass or graphite-resin composite, polyurethane, or a similar material, while the post is frequently formed of a hard material which is capable of supporting the rear foot under the high compressive loads which are developed at heel strike.
Such orthotic devices generally serve to both initially position the foot and then control the foot's motions as it progresses through the gait cycle, e.g., a normal foot should roll (frontal plane motion) about 4.degree.-6.degree. when walking, and perhaps 20.degree.-30.degree. when running. To control the motion of the foot, the plate member flexes resiliently to a controlled degree, and also there is often a need to impart a degree of rocking or eversion/inversion motion of the heel post as well, depending on the demands of the needs of the individuals foot/gait and the intended use. For example, for a high-impact running gait, it is often desirable to effectively increase the inversion of the rearfoot at heel contact, so as to increase the total amount of pronation and therefore the total amount of motion which is available for the balance of the gait cycle.
To adjust the rear foot angulation, and also in those instances where the heel post is supposed to move within the shoe, a common practice has been to grind off or otherwise remove material from the bottom of the heel post, in the area where this engages the insole. For example, FIG. 4 shows an exemplary prior art orthotic device 01, in which a portion of the heel post has been ground off to form a secondary planar surface 03 on the lateral underside of the post. This provides the post with a "bi-planar" bottom, so that it pivots through a controlled angle .theta..sub.0, from a first position in which the main bottom surface 04 rests generally flat on the plane 05 of the insole, to a second position in which the upwardly angled surface 03 rests on the insole: For example, at heel strike the rearfoot is generally inverted and the weight is borne mostly on the lateral side of the heel, so that the secondary surface 03 is pressed against the base plane 05, and then as the foot pronates and the weight shifts forwardly and medially, the device rocks onto the main post surface 04.
The purpose of the rocking motion of the heel post is to impart this motion to the plate member 06 which is mounted to the top of the post, the plate member being the component which actually bears against and engages the plantar surface of the person's foot. For several reasons, however, the operation of such devices is frequently less than satisfactory.
For example, achieving the correct pivoting motion is highly dependent on the engagement between the bottom surface of the post and the underlying insole, but the contours of most insoles tend to be irregular and vary greatly from shoe to shoe; in an effort to provide a uniform surface for the post, some practitioners have resorted to filling in the heel area of the insole to provide a more or less flat, uniform surface, but this is an expensive and time-consuming process, and also modifies the shoe so that in some instances it can no longer be used without the orthotic.
Furthermore, the rearward portion of the device must have sufficient clearance between it and the interior of the shoe to allow for the pivoting motion (or else the edge of the device will rub against the inside of the shoe), but where the heel counter of the shoe is particularly tight it may not be possible to establish this clearance, at least without having to modify the device to the point where it is ineffective or uncomfortable to wear. Even in those instances where the heel counter is sufficiently large or loose to accommodate the device, time-consuming trimming and grinding of the device is often necessary to establish the proper motion.
Moreover, even when such devices do function as intended, the results have generally been less than ideal from a biomechanical standpoint. In particular, the pivoting motion of the post, back and forth between the two positions, is somewhat abrupt and irregular in nature, whereas a smoother, more uniform motion would be preferable from the standpoint of both function and user comfort.
Yet another problem which is inherent in conventional posted orthotic devices of the type which has been described above is that fabrication of the built-up structure is notably labor-intensive and expensive from a manufacturing perspective. As was noted above, the plate is frequently formed of a thin, hard material, such as fiberglass or graphite-fiber resin material, while the post is commonly formed of hard rubber or something similar. In order to establish a bond between these two components which will be sufficiently strong and durable to withstand repeated impacts and distortions without separating frequently requires the use of relatively specialized and expensive adhesive compounds. Moreover, extensive and painstaking surface preparation is often necessary in order for these adhesives to work properly, typically involving grinding or otherwise abrading one or both surfaces, applying both primary and final coats of adhesive, heating the components in an oven, and so on. As a result, the need to fixedly mount the post to the orthotic plate adds significantly to the cost of the product.
Accordingly, there exists a need for an orthotic device in which the motion of the plate member which engages the plantar surface of the foot is generated independently of and without being affected by any irregularities or differences in contour which may exist in the heel area of a shoe insole. Furthermore, there exists a need for such an orthotic device in which such motions in a significantly smoother, more uniformed manner. Still further, there exists a need for such an orthotic device which eliminates the need for gluing or otherwise mounting the post and orthotic plate to one another.